This invention relates in general to processes for producing bio-ethanol, and in particular to an improved process for producing bio-ethanol from a lignocellulosic material.
Since the development of internal combustion engines and automobile mass production by Henry Ford there has been interest in ethanol. Clean burning, higher octane than gasoline, ethanol had been Ford's original choice of fuel for the Model “T”, but then (and for the past 75 years) fossil fuels became the dominant source of portable energy for industry and consumers. The result has been a polluted world, dependance on foreign nations for energy supplies and ever increasing costs as fossil fuel sources are depleted.
Ethanol, a naturally renewable fuel source, has generated immense interest over the past 10–15 years. The move to ethanol-enriched cleaner fuels, which eliminate or reduce the polluting and carcinogenic additives required to enhance gasoline, has produced a huge and increasing demand for ethanol around the world. In much of North America, 10% ethanol in gasoline is the standard, and in other countries such as Brazil, E-85 (85% or more ethanol) is the new standard. Clearly, as fossil fuels disappear, this new technology is the energy source of future.
With the increasing cost of oil and gasoline and the development of other ethanol markets, corn- and grain-based ethanol production has gradually become commercially viable. There is tremendous growth forecasted in this area over the next 10 years as the gradual fuel conversion to E-85 and environmental-based demands for ethanol increase. Most Canadian ethanol plants are in the process of dramatically expanding their production facilities.
Presently, almost all bio-ethanol production facilities in North America are corn- or grain-based. They grind up starch/carbohydrate rich corn/grain, treat this with a complex process to break this substrate into sugars (primarily glucose), and then ferment the sugars into ethanol (with the by-product of CO2) for industrial/commercial and medical uses.
The technology advances in these corn/grain production based industries have gradually reduced the, cost of ethanol to current levels, but they have reached a “wall” which is related to the availability and cost of their “substrate”, corn or grain. A major expense and uncontrollable factor will always be the price of corn/grain and the fact that the process substrate is “food” for animals or humans and in limited supply. Certainly, the supply is far too limited to allow for the competing worldwide demand for both food and bio-ethanol in the future.
These conclusions have prompted nationwide efforts in Canada and the USA over the past 10 years to investigate and develop technology to produce ethanol from lignocellulosic biomass (e.g., wood chips, leaves, corn stover, straw, bagasse, rice straw, and municipal cellulosic waste). In a typical lignocellulosic biomass process, substrate primarily composed of cellulose is ground up and then pre-treated (usually with acid) to break down the cellulose and separate the three main components of wood (cellulose, hemi-cellulose and lignin). These components are then acted upon by catabolic enzymes to form a fermentable mixture of glucose and xylose (the basic component of hemi-cellulose), and this is then fermented and distilled to create ethanol.
The intrinsic advantages of this process are that there is a virtually unlimited supply of lignocellulosic biomass of many types, it is fully renewable and natural, and it is cheap. In fact, many potential sources of lignocelluosic biomass actually generate revenue for the process due to their present disposal costs. Bio-ethanol production is relatively environmental friendly, as much of this feedstock material is burned, ploughed under or composted. However, based on present technologies, the current cost/gallon for bio-ethanol remains high in relation to fossil fuels. Lignocellulosic bio-ethanol production simply costs too much, because the basic “substrate” materials (wood, non-woody lignocellulosic feedstock) are difficult and expensive to break down into fermentable materials. Consequently, there are presently no commercial lignocellulosic biomass to ethanol plants in North America.
There is an extensive patent literature relating to de-lignification of lignocellulosic materials, predominantly relating to applications in the pulp and paper industry. For example, bleaching of lignocellulosic materials in the presence of oxygen and peroxide has been described in U.S. patents such as Farley U.S. Pat. No. 3,719,552, Tyson U.S. Pat. No. 4,842,877, Phillips U.S. Pat. No. 4,372,812, Paren U.S. Pat. No 6,165,318, Francis U.S. Pat. No. 4,729,817, Miller U.S. Pat. No. 6,162,324, Forslund U.S. Pat. No. 6,221,207, Call U.S. Pat. No. 6,103,059, Miller U.S. Pat. No 5,916,415, Gould U.S. Pat. No. 4,649,113, Singh U.S. Pat. No. 4,196,043, Foody U.S. Pat. No. 6,090,595, Holtzapple U.S. Pat. No. 5,865,898, Ladisch U.S. Pat. No. 5,846,787, Klyosov U.S. Pat. No. 5,777,086, and in U.S. patent applications such as Forslund 2001050152, and Pat 20010025695. The described processes focus on improvement in de-lignification during bleaching of paper pulps with retention of viscosity index (indicative of cellulose strand integrity/predictive of paper strength). The primary goal of these de-lignification process improvements has been to avoid the negative aspects of various pretreatments used in the pulp and paper industry, specifically to de-lignify with reduced disruption of the cellulose polymer structure. Most of this work is not related to pretreatment during bio-ethanol production.